The interaction between a structural element, for example of an aircraft and spacecraft, and an air flow is known as aeroelastics and the behaviour of the structural element in the air flow is known as the aeroelastic behaviour of the structural element. The aeroelastic behaviour of the structural element, in particular a mode shape of the structural element, is determined, inter alia, by the rigidity of the structural element. The term “mode shape” is understood as meaning the shape of the structural element assumed by the structural element under a vibration load, for example. The structural element is not only subjected to structural-dynamic effects but also to elastic deformations as a result of air flows. The elastic deformations are a result of the structural-dynamic characteristics as well as of the aeroelastic characteristics of the structural element and can lead, for example, to undesirable vibrations of the structural element. In turn, this can cause an increased generation of noise, a partial loss of function of the structural element, such as in the case of fluttering of a control surface, or can even cause the structural element to rupture or disintegrate.
The Applicant is familiar operationally with various procedures for influencing the aeroelastic characteristics of the structural element. Additional masses are often attached to an affected structural element, as a result of which it is possible to influence the natural vibration frequencies of the structural element, for example. Although this procedure produces good results in respect of the vibration behaviour of the structural element, it is a disadvantage that unnecessary masses, i.e. so-called dead or unsupporting masses have to be moved during operation of the aircraft and spacecraft. This leads, inter alia, to the disadvantage of increased fuel consumption due to the excess weight.
Alternatively, it is possible to adapt the rigidity by adapting shapes of the affected structures or, in the case of fibre composite construction methods, by appropriately varying the fibre orientations and layer structure. However, it has been found that a disadvantage of this procedure is that the shape, which is optimised in respect of lightweight construction, strength and aerodynamic behaviour, of the structural element has to be changed. Changing the fibre direction orientation and/or the layer structure also means a change which is undesirable in respect of the achievable mechanical characteristics and an increased expense in adapting the corresponding component shapes.
Furthermore, it is possible to vary the materials which are used. For example, materials which have different rigidity and/or strength characteristics can be incorporated into a structural element. However, this greatly increases the production costs and outlay.
It is also possible to use passive or active damper elements. However, the use of damper elements means an increase in the number of components of the structural element. This presents the disadvantage of additional weight and furthermore adversely increases the complexity of the structural element.
DE 698 05 302 T2 describes, for example, a structural element for an aircraft and spacecraft, the rigidity of which can be actively changed. For this purpose, an effective cross section of the structural element and thus the rigidity thereof is changed by means of a piezoelement integrated into the structural element. The piezoelement arranged in a recess in the structural element is moved from an unexpanded state into an expanded state, the piezoelement only resting against two opposing walls of the recess in the expanded state and thus transferring forces from one wall to the other. This measure changes the rigidity of the structural element and the aeroelastic characteristics thereof can thus be actively influenced. However, this approach to solving the problem requires the use of additional components which also unfavourably involve an increase in the complexity and probability of failure of the structural element in addition to an extra weight.